The overall objective of this research is to determine the mechanism by which hypertension is caused and aggravated by oral contraceptives. A study will be made of the effects of these drugs on the levels of norepinephrine (NE), which causes vasoconstriction and increases blood pressure (B.P.), in sympathetically innervated organs and regions of brain of normotensive and genetically hypertensive rats. Attempts will also be made to determine the mechanism of possible changes in circadian (24-hour) rhythms in NE in these organs and brain regions following administration of these drugs. BIBLIOGRAPHIC REFERENCES: Lew, G.M. (1976). Circadian rhythms in blood pressure and norepinephrine in genetically hypertensive and normotensive rats. General Pharmacology 7, 35-40. Lew, G.M. (1977). Temporal differences in the effects of amphetamine on norepinephrine. General Pharmacology (in press).